1. Field of the Invention
This invention relates to digital signal processing, and more particularly, but not exclusively, to apparatus for extracting synchronizing information from serial-bit digital television signals on reproduction from a digital video tape recorder (VTR), and for de-serializing the digital signals in dependence on the synchronizing information.
2. Description of the Prior Art
Almost irrespective of the way in which a television signal is processed and coded prior to recording on a digital VTR, the signal actually recorded is a serial-bit data stream comprising video data, error protection information, spare data capacity which may be used for example to record items such as dates, times and titles, and synchronizing information. The synchronizing information is crucial to recovering the data on reproduction. Thus whilst the VTR is synchronized to the system video, the mechanical tolerances of the VTR result in the timing on reproduction varying with respect to the system video. The reproduced synchronizing information is therefore essential to enable the reproduction processor to recover the data. On recovery, the data can be temporarily stored and read from the store in synchronism with the system video.
Moreover, because the data stream which is recorded and reproduced is in serial form and the reproduced data stream must be converted to parallel form in the reproduction processor, the synchronizing information is used to identify individual words in the reproduced serial data.
The recorded data stream is generally in the form of blocks of words, and in summary, therefore, on reproduction the synchronizing information is required to enable identification of the first bit of each word so as to permit de-serialization, and is also required to enable identification of the first word of each block of data words.